Sound pickup device



April 1944. M. RETTINGER 2,346,395

SOUND PICKUP DEVICE Filed May 4. 1942 J IC'HAEL KETT/NGE/E,

INVENTOR F B g/KM A TTORNE Y Patented Apr. 11, 1944 Pewr I This invention relats'to electro-acous'ticalap paratus -an'dfmore {particularly to -'microphones of the ribbon type, such"a s"-shown-iri-U. S. Patent No. 2,141,420 or ec mber-e7,i933; and copending application- 86i". Noi" 270,801 of H.

filed April 29, 1939.

It is well known that in the 'velocity ribbon type microphone, as wellas the pressure-ribbon type mirophone the ribbon launder a light tension in order to'pla'ce the resonant peak of the ribbon near the lower extremity of the audible frequency range. The lower the amplitude of this 1 resonant peak' and the n'eareriti's' to the lower extremity of the audible frequency range without encumberingits motion, the better the microphone response characteristic obtained.- In the above-mentioned copending application's. flat silk screen across *the pole pieces of" the velocity ribbon is used'to'provide an acoustic impedance orresistance which reduces the amplitude of the resonant peak and moves it nearer i the lower end I of the audible frequen'cyra'nge. The present invention is directed to thisforni ofconstruction to provide an acoustic:- impedance in combination with an additional function, I I

w r The ribbons lof the microphone: mentioned :1 i above are generally-corrugated and suspended in the airgapformed by and between tapered pole pieces. The ribbon is necessarily loosely suspended 'andiis easily displaced from the air gap by g sts of wind or loud, sharp sounds, such as pistol shots and the like. Such displacement is, of course, deleterious to the operation of the microphone and may in many cases injure the ribbon itself. The use of a single screen as shown in the above-mentioned application has been found. to provide insufficient protection for the ribbon under actual sound recording conditions, the present invention not only providing such protection under abnormal conditions but also providing a better frequency response characteristic for the microphone. By the use of an additional silk screen or screens which are attached by cementing and th like to the tapered sides of the pole pieces, the apices of the creens may be positioned in close proximit to the microphone ribbon or ribbons. The screen may be used on one or both sides of the ribbon, depending on whether the microphone is a pressure or pressure gradient operated device, respectively. The flat screen of the above-mentioned application may or may not be used in conjunction with the V-type screen, the combination reducing wind noise efiects.

The invention is also applicable to the uni-diol on,

UNI? ED ATE'NT OFFICE IINPLH UH D VICE i 'chael.ltettinger, Encino Cali! assignor to Radio CorporationotAmerica, a corporation oi Application 4, 1942, S erial l\l0. 44159 1,. y claim (Ci. ll

" rection'al' type of microphone wherein one of the "dual ribbons of the microphone is provided with an acoustical impedance or resistance in the form of a chamber, as shown in the above-mentioned Patent No. 2,141,420, or as shown in the abovementioned copending application, in the form of a tube or pipe filled with hair felt.

1 The principal object of the invention, there- 1 fore, is to improve the frequency response characteristic of aribbon type microphone and to protect the ribbon from gusts of wind.

Another object of the invention is to provide frequency range'at the lower end of the audible spectrum.

Afurther object of the invention is to provide a combined ribbon protector and acoustic resistance for a microphone, which will provide a smooth frequency response and reduc the collection of dirt in narrow air gaps.

it Although the novel features which are believed tobe'characteristic of this invention are pointed out with particularity in the claims appended herew1th,.the manner of'it organization and the mode ofits operation will be better understood by referring to the following description read in conjunction with the accompanying drawing,

forming a part hereof, in which:

Fig. 1 is a front elevational view partially in section of an acoustic device embodying the invention;

Fi 2 is a, side elevational view of the device of Fig. 1 taken along the line 2-2 thereof, and

Fig. 3 is a cross-sectional view of the invention taken along the line 3-3 of Fig. 1.

Referring now to the drawing in which the same numerals refer to like elements, a base sectlon 5 generally housing a transformer supports a pair of U-magnets 6 and 1, the magnets being provided with tapered pole pieces 9 and I0, an an gap being formed between the truncated ends 01 the pole pieces (see Fig. 3).

Mounted within the U-portion of the magnet 1 and bridged across the pole pieces is a ribbon clamp i2 and within the U-portion of the magnet 6 is a clamp i3 mounted on an adjustable support l5 adapted to be adjusted by screws I6 and I1. Supported between the clamps l2 and I3 is a corrugated ribbon 20, the proper tension being placed therein by the adjustment of the support [5.

Surrounding the entire structure is a wire wind screen 22, the assembly being mounted on pivot screws 23 and 24 and a yoke, the legs of which are shown at 25 and 26. For further protection of the ribbon, screens 29 and 30 are shown positioned on either side of the ribbon at some distance therefrom.

The above microphone is a standard commercial equipment unit known as a velocity microphone. The construction embodying the invention comprises the finely-woven V-shaped silk screens shown at 32 and 34. Although the screens 32 and 34 are generally suiiicient to provide the desired protection and acoustic resistance, further protection can be obtained by the use of flat silk screens 35 and 36 across the base of the pole pieces. The screens 32 and 34 are cemented, glued or otherwise firmly attached to the tapered sides of the pole pieces 9 and In, the apices 39 and 40 of the V-screens being adjacent the ribbon 20, so that the ribbon barely clears them as shown in Figs. 2 and 3. This adjustment is suflicient to provide the ribbon with all the movement required for the optimum generation of an electro-motive force by sound waves actuating the ribbon.

By this method of and means for applying the silk screens 32 and 34, the necessar acoustical resistance is obtained to provide a particularly desirable frequency response characteristic while simultaneously providing the optimum protection at the ribbon 20. By the use of the additional screens 35 and 36, air motion is impeded before striking the screens 32 and .34 and consequently the ribbon 20, thus reducing the velocity of its movement against the screens 39 and 43. The use of the flat screens 35 and 35 also improves the frequency response characteristic, and reduces the collection of dirt in the air gaps, although the use of these screens is not necessarily required.

I claim as my invention:

1. An electro-accustical device comprising means for producing a magnetic field, a vibratile element mounted for movement in said magnetic field, said element having an optimum degree of excursion in said field, and means for simultaneously providing an acoustical impedance for said vibratile element and for limiting the excursion of said element within said field.

2. An electro-acoustical device in accordance with claim 1 in which said last-mentioned means comprises a shield in close proximity to said element.

3. An electro-acoustical device comprising a magnet, a pair of tapered pole pieces for said magnet, said pole pieces providing an air gap between the truncated apices thereof, a vibratile element in said air gap and adapted to be moved therein by air waves, said element having a safe excursion of definite limits, and means on at least one side of said vibratile element for maintaining said element within said limits while maintaining the resonant frequency oi said element below a predetermined value.

4. An electro-acoustical device comprising a magnet, a pair of tapered pole pieces for said magnet, said pole pieces providing an air gap between the truncated apices thereof, a vibratile element in said air gap and adapted to be moved therein by air waves, said element having a safe excursion of definite limits, and means for maintaining said element within said limits, said element comprising a corrugated ribbon lightly tensioned within said air gap, said last-mentioned means providing an acoustical impedance for said ribbon.

5. An electro-acoustical device in accordance with claim 3 in which said last-mentioned means comprises closely woven silk shields attached to the tapered sides of said pole pieces and having their apices within said air gap closely adjacent said element.

6. An electro-acoustical device in accordance with claim 3 in which said last-mentioned means comprises V-shaped shields of silk attached to the tapered sides of said pole pieces and fiat silk shields spanning the bases of said pole pieces.

7-. An electro-acoustical device comprisin a plurality of magnets, truncated triangle pole pieces for said magnets, said pole pieces forming an air gap therebetween, a ribbon suspended in said air gap, a wind screen surrounding the above mentioned elements, and V-shaped silk shields attached to the tapered sides of said pole pieces, the apices of said shields being positioned closely adjacent the sides of said ribbon to limit the excursion of said ribbon, said shields also providing an acoustical impedance for said ribbon.

MICHAEL RE'I'IINGER. 

